The present invention relates, in general, to the cleaning of flue gas and, in particular, to a new and useful device for deflecting a slurry flow away from an inlet transition between an inlet flue and a housing of a wet scrubber module which serves to keep the inlet dry and thereby minimize deposition.
FIG. 1 is a schematic representation of a portion of a known wet flue gas desulfurization (FGD) system 10, wherein a wet scrubber module 12 having a cylindrical housing 14 receives a flue gas 16 at a transition between an inlet flue 18 and the housing. Inlet flue 18 typically approaches cylindrical housing 14 at a downward angle ranging from 0.degree. to 90.degree. from the horizontal. Inlet flue 18 is typically rectangular in cross-section, having a width W that is approximately 2.5 times greater than its height H (i.e., an aspect ratio of width to height W/H of approximately 2.5 ). At locations 20, 22 near an intersection of upper and lower surfaces 24, 26, respectively of inlet flue 18 and cylindrical housing 14, inlet flue 18 is mitered so that it intersects and attaches to cylindrical housing 14 at a 90.degree. angle; i.e., inlet flue 18 is substantially perpendicular to cylindrical housing 14. This perpendicular orientation simplifies the transition, structural design and fabrication of the wet scrubber module 12. Prior to inlet flue 18, other portions (not shown) of the flue system upstream of inlet flue 18 may include cross-section transitions, elbows, fans, and/or other hydraulic devices to supply the flue gas 16 to the inlet flue 18.
As illustrated in FIGS. 2 and 3, within the cylindrical housing 14, an inlet awning 28 is used to direct part of the hot flue gas 16, typically provided to the wet scrubber module 12 at a temperature of approximately 300.degree. F., downwardly at a 45.degree. angle with respect to horizontal. Liquid slurry 30 that is sprayed within the wet scrubber module 12 and/or which drains from packing, trays, or other surfaces within the wet scrubber module 12, flows downwardly onto an upper surface 32 of the inlet awning 28. A weir plate 34 located above a tip 36 of the inlet awning 28 provides a gap 38 through which liquid slurry 30 passes, and thus regulates and improves the uniformity of a liquid slurry curtain 40 that is discharged down into the hot flue gas stream 16. As the hot flue gas 16 enters the wet scrubber module 12, it is quenched and humidified by the liquid slurry curtain 40, evaporating a fraction of the water present in the liquid slurry curtain 40.
In the absence of an inlet awning 28, a thin liquid film of liquid slurry 30 flowing downwardly along the walls of the wet scrubber module 12 contacts the hot flue gas 16. However, the amount of water present in the thin liquid film of slurry 30 falling across the inlet opening to the wet scrubber module 12 is not sufficient to completely quench and humidify the hot flue gas 16. The inlet awning 28 collects all the liquid slurry 30 that falls on top of it and channels the liquid slurry 30 to the gap 38 to form the thick liquid slurry curtain 40. This larger amount of water diverted by the inlet awning 28 and forming the liquid slurry curtain 40 exceeds what is needed for complete and instantaneous quenching and humidification of the hot flue gas 16. This complete and sudden quench and humidification reduces the wet/dry interface and the possibility of solid deposition.
In the absence of an inlet awning 28, if the liquid slurry 30 and hot flue gas 16 combination contacts arty surface of the inlet flue inlet 18 or housing 14, solid deposits will form as the liquid slurry 30 evaporates. Solids form at the wet/dry interface because the water present is not sufficient to continuously and fully humidify the incoming gas. These solid deposits build up over time, which requires the wet scrubber module 12 to be shut down so that maintenance personnel can enter the wet scrubber module 12 and remove the deposits. Shut down of a wet scrubber module 12 requires that either spare wet scrubber modules 12 be available to clean the flue gas 16, reduced boiler load so that the amount of flue gas produced does not exceed the capacity of the remaining on-line wet scrubber modules 12, or discharge of partially or untreated flue gas 16 directly into the atmosphere. All of these alternatives are undesirable and not accepted by the industry. It is thus preferable to maintain the wet/dry interface of the liquid slurry 30 with the hot flue gas 16 away from these surfaces, and the inlet awning 28 accomplishes this result by creating the liquid slurry curtain 40. The liquid slurry curtain 40 is maintained away from these surfaces because the inlet awning 28 extends downwardly and into the cylindrical housing 14 of wet scrubber module 12. The liquid slurry curtain 40 also provides more water than required for humidification.
As shown in FIGS. 4 and. 5, at the side ends 42 of the inlet awning 28, sidewalls 44 extend from the inlet awning 28 into the housing 14 and downwardly to a point below the lower surface 26 of inlet flue 18. These sidewalls 44 prevent liquid slurry 30 from flowing off the side ends 42 of the inlet awning 28 or along an inner surface 46 of the housing 14 from entering inlet flue 18. These sidewalls 44 are necessary to maintain an acceptable wet/dry interface away from these surfaces to avoid the deposition problems discussed earlier. In addition, the inlet awning 28 is provided with stiffeners 48 which, in conjunction with the sidewalls 44, further distribute the slurry flow 30 evenly about these surfaces.
Hydraulic testing of the known inlet flue 18 and inlet awning 28 devices described above revealed a significant flue gas side total pressure drop. High flue gas side pressure drops require increased fan pressure capability, resulting in increased fan and motor capacity and increased operating costs for the life of the unit. This is very undesirable because even a 1.0 inch H.sub.2 O gas side pressure drop can be assessed at values which can reach one million dollars. Therefore, reducing the flue gas side pressure drop in the wet scrubber equipment is an effective way to reduce costs. However, such reductions must still be achieved in a manner which prevents unwanted deposition of dried slurry material at the transition.